Drop the requirement for system-wide kernel UAPI headers to provide full struct btf_enum64 definition. This is an unexpected requirement that slipped in libbpf 1.0 and put unnecessary pressure ([0]) on users to have a bleeding-edge kernel UAPI header from unreleased Linux 6.0. To achieve this, we forward declare struct btf_enum64. But that's not enough as there is btf_enum64_value() helper that expects to know the layout of struct btf_enum64. So we get a bit creative with reinterpreting memory layout as array of __u32 and accesing lo32/hi32 fields as array elements. Alternative way would be to have a local pointer variable for anonymous struct with exactly the same layout as struct btf_enum64, but that gets us into C++ compiler errors complaining about invalid type casts. So play it safe, if ugly. [0] Closes: https://github.com/libbpf/libbpf/issues/562 Reported-by: Toke Høiland-Jørgensen <toke@xxxxxxx> Fixes: d90ec262b35b ("libbpf: Add enum64 support for btf_dump") Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> --- tools/lib/bpf/btf.h | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h index ae543144ee30..8e6880d91c84 100644 --- a/tools/lib/bpf/btf.h +++ b/tools/lib/bpf/btf.h @@ -486,6 +486,8 @@ static inline struct btf_enum *btf_enum(const struct btf_type *t) return (struct btf_enum *)(t + 1); } +struct btf_enum64; + static inline struct btf_enum64 *btf_enum64(const struct btf_type *t) { return (struct btf_enum64 *)(t + 1); @@ -493,7 +495,28 @@ static inline struct btf_enum64 *btf_enum64(const struct btf_type *t) static inline __u64 btf_enum64_value(const struct btf_enum64 *e) { - return ((__u64)e->val_hi32 << 32) | e->val_lo32; + /* struct btf_enum64 is introduced in Linux 6.0, which is very + * bleeding-edge. Here we are avoiding relying on struct btf_enum64 + * definition coming from kernel UAPI headers to support wider range + * of system-wide kernel headers. + * + * Given this header can be also included from C++ applications, that + * further restricts C tricks we can use (like using compatible + * anonymous struct). So just treat struct btf_enum64 as + * a three-element array of u32 and access second (lo32) and third + * (hi32) elements directly. + * + * For reference, here is a struct btf_enum64 definition: + * + * const struct btf_enum64 { + * __u32 name_off; + * __u32 val_lo32; + * __u32 val_hi32; + * }; + */ + const __u32 *e64 = (const __u32 *)e; + + return ((__u64)e64[2] << 32) | e64[1]; } static inline struct btf_member *btf_members(const struct btf_type *t) -- 2.30.2
